<!DOCTYPE html>
<style>
.red { color: red; }
</style>
<script>
document.onreadystatechange = function() {
  if (document.readyState == "complete") {
    var arr = ["s2","s3"];
    arr.forEach(function(n) {
      document.getElementById(n).className = "red";
    });
  }
};
</script>
<div>
  <span id="s1">test</span><br />
  <span id="s2">test</span><br />
  <span id="s3">test</span><br />
  <span id="s4">test</span><br />
</div>
